This invention relates to equipment for stretch band wrapping pallet loads with stretch film.
Various machines are presently marketed for stretch band wrapping palletized loads with a stretchable polymer. Multiple layers of the polymeric film are wrapped around the load by rotating the load on a platform while restraining the film feed to cause the film to stretch and wrap tightly. The film is supplied from a roll of film initially having a diameter of several inches, typically about 8 to about 20 inches in diameter. The width of the roll or rolls can vary from about 20 inches to 110 inches. The roll is usually positioned on a vertical spindle parallel to the rotational axis of the pallet load.
One known technique for restraining the film is to apply a constant torque braking force to the central rotating spindle that mounts the roll of film. But, as the roll of film decreases in diameter, the tension on the film extending from the periphery of the roll to the load increases. This is undesirable. Because of this characteristic, another technique sometimes employed is that of pressing a plurality of spaced braking wheels against the outer surface of the film roll. But the web portions between the wheels are subjected to different tensile forces than those portions engaged by the wheels, thereby applying undesired diagonal tension forces to the film.